For this you need create a variant for the job to be run with the following parameters

DEL_MSG 30 – delete all records older than nnn day (M-Records)
DEL_PAR 30 – delete all records older than nnn day (R- and P-Records)
DEL_DTP ‘ ‘ – useless/no function (unused parameter as of SAPKW73004, you can see that in the)

(note that not entering parameters or entering 1 or 2 as DEL_MSG/DEL_PAR defaults to deleting records older than 180 days).